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SAQ, Grimeton Transmission 17.2 kHz 24th of Oct




 
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Author Topic: SAQ, Grimeton Transmission 17.2 kHz 24th of Oct  (Read 626 times)
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SM6OID
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« on: October 20, 2020, 04:15:10 PM »

Hi!

So, once again the old alternator will start to rotate...

https://alexander.n.se/saq-grimeton-transmission-on-october-24th-2020/
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RADIO: 51J-4, R-390A, SP-600 JX-21, BRT-400, Set No 19, T-47/ART-13, RF-590, SRT CR91, BC-312D, BC-348Q, HF-8020/8030/8010A/8090,  and much more...

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« Reply #1 on: October 20, 2020, 11:47:25 PM »

The website is wonderful, what a fantastic transmitter and antenna system, great historical preservation.
At 17.2 KHZ CW, I was reading about the up-converters people use to hear the signal, I wonder what would be a simple
receiver system to hear the signals? I guess I need to learn more about VLF systems, etc.. Great subject.
I would love to see that thing in operation, fantastic!
Donnie
AG5UM
P.S.  I see on their forum people discussing VLF-"ULF" systems and "ground-probe" antennas, interesting things.
       maybe, at those frequencies you could just put your ear to the ground and hear them....interesting, fun stuff.
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W2JBL
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« Reply #2 on: October 24, 2020, 12:03:05 AM »

Ready to go here with an Alinco Dr-SR8 ricebox fed with a Plaomar VLF converter. Antenna is a Beverage on the ground- 800 feet of wire on the forest floor not terminated. I can hear all the US navy stations on 20, and 24.8, 40, and WWVB 60 KHZ with big signals. Heard QRM from another station on 17.2 running data friday morning. Hope it's not there during the broadcast.   
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AJ1G
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« Reply #3 on: October 24, 2020, 05:54:42 AM »

Will try to head over to Watch Hill Point to copy the broadcast using my Wandell und Goltermann  AT-611 Selective Level Meter and the 75 meter Hamstick on the Volvo XC60 roof.   Copied the early July Alexanderson Day broadcasts using that setup from Watch Hill  Point and Weekapaug Point. Will also try using a loop antenna which is actually an old TV degaussing coil, gave it a trial run this morning and it received the Navy VLF stations on the AT-611with very good SNR, although actual dBM levels were lower than using a large wire antenna.

To keep background noise from the Volvo minimized, I power the AT-611 from a small 100 watt 12VDC to 120VAC converter and a small 12V jump start battery pack.  It only draws about a 25 watts despite weighing about 80 pounds.  The inverter is very quiet at VLF, but awful on HF.  

To copy SAQ, you have to be in a very low noise location.  If you can receive NPM Oahu on 21.4 kHz with good SNR, you should have a good chance of copying SAQ.  

Try to follow the broadcast on their YouTube livestream while you are trying to tune in.  Even if you canít receive it directly, the livestream of the start up and broadcast is well worth watching.  The actual message broadcast is only a few minutes long, but they will be sending  VVVs de SAQ for about a half hour as they bring the alternator on line.  Good luck trying.



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Chris, AJ1G
Stonington, CT
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« Reply #4 on: October 24, 2020, 11:57:24 AM »

Copied the entire SAQ transmission from first key down in tune up to end of message between about 1040 to 1105Z down at the Barn Island State Wildlife Reservation about 2 miles from the home QTH.  Was easy to tell when they started making RF by watching the YouTube livestream. There is a huge boat launch parking lot at Barn Island on the north shore of what is known as Little Narraganset Bay, the waters behind the Watch Hill RI Napatree Point barrier beach that extends to the west from Watch Hill Point.

VLF background noise levels at Barn Islandare among the lowest I have experienced around here, about -120 dBm In a 400Hz filter bandwidth.  No power lines closer than about a mile. SAQís CW signal was steady probably about +3dB above the steady state noise floor, however lightning static crashes were about +15 dB above the floor.  NWC in SW Australia, NPM on Oahu, and of course NAA  Cutler Maine, weíre all hammering in with huge SNRs

Iíve never done any serious HF mobile DXing from here but I definitely will be doing some very soon, will need to check the CT DEM website re access at night.


* A974CD58-0064-4014-B73C-E3CF616ABC45.jpeg (2680.3 KB, 4032x3024 - viewed 56 times.)
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Chris, AJ1G
Stonington, CT
SM6OID
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« Reply #5 on: October 24, 2020, 01:46:53 PM »

Hi!
Chris, nice to hear that you copied the transmission!
My location is not far away from Grimeton, slightly less than 100 miles, so the signals were strong!
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RADIO: 51J-4, R-390A, SP-600 JX-21, BRT-400, Set No 19, T-47/ART-13, RF-590, SRT CR91, BC-312D, BC-348Q, HF-8020/8030/8010A/8090,  and much more...

ENGINE: Zvezda M50 F6L (V12), Rolls-Royce Meteor mk4B/2 (V12), Rolls-Royce B80 (inline 8 ) and much more
AJ1G
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« Reply #6 on: October 25, 2020, 05:52:01 PM »

Just a quick follow up on using the old TV degaussing coil as a VLF receiving loop antenna.

I didnít actually use it during the SAQ transmission.  I did a quick try but it was being hammered by EMI from the 100 watt DC to AC inverter powering the W und G selective
level meter, which were not detected when using the Hamstick.  Apparently it was a very near field proximity effect.  I later tried mounting the loop on the roof of the Volvo and had very good results, listening to the other usual VLF signals. Received levels on the loop for NAAís rockcrusher signal on 24 kHz were 6 dB higher with the loop vs the Hamstick, and similar to levels observed when using a 80 meter dipole at home.   More importantly, as expected, the loop exhibited an extremely sharp and deep (nominal 24 dB on NAA) directive null, which permitted much better SNR on the next signal up the band at 25.2 kHz (NLK in Washington State IIRC).  Although I didnít try, it would likely have reduced the levels of t-storm static that was observed when trying to copy SAQ.  Did a little more playing around with it today and found placing the loop a couple of feet above the car room resulted in further signal level increases.

I didnít try to resonate it, just used it directly into the bridging mode input of the SLM.  Will try resonating it next. Will also see how it plays at higher frequencies such as at 630 meters, BCB, and 160 meters.

Key take away - you may have a pretty good receiving loop antenna in your junk box, or should keep an eye out for one under the tables if we ever will have real hamfest swap meets again, disguised as an old school TV degaussing coil.
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Chris, AJ1G
Stonington, CT
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« Reply #7 on: October 26, 2020, 03:30:15 PM »

So, I missed this one due to lack of receiving equipment..But I'd like to try to hear the next one.

So I was thinking, how can I receive this?  Once picked up by an antenna, it is essentially AC at audio frequencies. I was thinking to connect an antenna directly to a microphone preamp and then through an audio dsp (I have multiple preamps and dsp to choose from).

Typical midgrade professional mic pres have an EIN of -129dBu, or about 0.3uV.  Where does that sit in comparison to received levels from an antenna of VLF signals? If I did this would there be any chance the signal would be above the preamp noise?

Now, I haven't been able to hear 17.2kHz for a long time. Besides having a childhood passion for homemade fireworks, I spent the late '80s and most of the '90s running sound for rock concerts. My once-long hair has disappeared, taking some of my hearing along with it....  I figured, however, I could take this received signal in the DSP, add a 16.8kHz tone to it, and hear the resulting 400Hz product just fine. It is also easy to set up a a VERY narrow filter around 17.2kHz in the DSP.   Any thoughts on how well this would work?

Finally, what about an antenna?  A loop? I'm guessing I'd want a coil on the order of millihenries..

Ed
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Ed, K8DI, warming the air with RF, and working on lighting the shack with thoriated tungsten and mercury vapor...
AJ1G
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« Reply #8 on: October 27, 2020, 12:39:50 PM »


Ed - would be interested in hearing about your results.  I suspect that you will need a some sort of high pass cut off filter to reject any electrical harmonic interference  from lower frequencies which would likely overload your detection processing. As I noted above, for starters as an antenna, you might try an old TV picture tube degaussing coil.  For clarification, I'm talking about the coils used by a serviceman that weigh a  couple of pounds with a line cord that is plugged into an AC outlet, not the small ones that were usually permanently installed on the back side of the picture tube within the TV set.
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Chris, AJ1G
Stonington, CT
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« Reply #9 on: October 27, 2020, 02:26:01 PM »


Typical midgrade professional mic pres have an EIN of -129dBu, or about 0.3uV.  Where does that sit in comparison to received levels from an antenna of VLF signals? If I did this would there be any chance the signal would be above the preamp noise?

The only way to know is give it a try!

A while back I tried using my NooElec RTL SDR 25 MHz+ dongle and NooELec HamIt Up 5kHz to 25 MHz upconverter to copy VLF signals  in the 15 -100 kHz region of the spectrum. System electrical noise floor was very high at those frequencies, and I could only see a small discrete at 24 kHz from NAA.  Used the 20 dB amplifier on my Ballentine 300G AC voltmeter, which is provided with an output jack on the meter front panel, to lower the noise floor that many dB which
allowed successful detection of a number of VLF signals.  IIRC the preamp was useable out to at least 500 kHz.
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Chris, AJ1G
Stonington, CT
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